The major effort this year has been concerned with development, validation, and application of methods for the accurate and reliable determination of chlorinated bibenzo-p-dioxins and bibenzofurans at low levels in environmental samples. Emphasis has been placed on accurate quantification and highly specific qualitative identification. Methods for extraction and cleanup of soil, adipose tissue, and liver have been developed and refined. A collaborative, study has been started involving ten laboratories in three countries, to compare the analytical capabilities of these laboratories (which all use different techniques and approaches) for the low part-per-trillion level measurement of a series of dioxins and furans in human adipose tissue. The most reliable analytical approaches should be identifiaable as a result of this study. Analysis of animal tissues and soil for 2,3,7,8-TCDD was used in another study to evaluate the bioavailability of TCDD bound to soil from Times Beach, Missouri.